The invention relates to an anchor-tie for carrying prefabricated concrete components.
An anchor tie of the above type is known for example from West German Offenlegungsschrift No. 19 13 912. In this anchor tie, there is a threaded part in the form of an internally threaded sleeve into which a rope loop can be screwed. The loop of rope is for connection with a lifting mechanism, which may, for example, be the hook of a crane. Instead of the loops of rope, it is possible to use other elements, such as, for example, eyebolts or similar.
The end of tie-rod, which may have rolled ribbing on its surface, is forced into the sleeve which is internally threaded at its outer end portion.
Another purpose of the threaded part of an anchor tie of this type is to secure the tie in the framework in which the concrete fabrication is produced. This ensures the correct positioning of the anchor tie.
It is known that the tie-rod can be made in various ways. For example, it is possible to use a bar of such length as to permit reliable transfer of forces to the concrete. As a rule, however, it transpires that relatively long lengths of rod are necessary for this.
If the tie-rod has, for example, a dish-shaped thickened portion, or a hook-shaped bend at its inner end, then the required length of rod can be reduced, since these devices improve the holding in the concrete to such an extent that the rod cannot readily be torn straight out. In the event of overloading, a cone-shape is far more likely to break out of the fabrication.
The provision of a thickened portion, for example by upsetting, is as a rule relatively expensive. If a hook shaped bend is to be produced, this presents the problem that certain radii cannot be exceeded when coldforming steel if one is to avoid the material of the rod being damaged as a result of the flexing action. Thus, a relatively large expansion perpendicular to the axis of the rod is permitted by a bent hook.
Now, if an anchor tie of this type is used in thin walled concrete fabrications, the plane of the hook can be adjusted in relation to the plane of the wall, but it is necessary to screw the anchor tie with its threaded part onto a corresponding bolt in the framework. The amount of space required by the hook proves very inconvenient when performing this fastening operation.
It is apparent that the carrying member must transfer very considerable forces during transportation of the concrete fabrication from the place of manufacture to the point of assembly, but after that the carrying member is no longer needed. It is therefore a `disposable` component which is required in great numbers and has therefore to be produced cheaply. DIN 529 describes masonry bolts which on the surface have a certain similarity to the construction of an anchor-tie.
However, in contrast with anchor ties for carrying masonry bolts are not used in the transportation of concrete fabrications, but are used at a later stage in the finished structure in bored-out holes and secured with mortar or some similar substance. Masonry bolts regularly break out of the hole with the plug of mortar in the event of overloading.
In the case of masonry bolts, various forms of anchorage elements are known which nevertheless are produced in relatively expensive forging operations.